The present invention relates to telephone switching systems, and more particularly, to conserving channel bandwidth in a communications link between a primary office and a remote location.
The majority of in-house telephone systems (e.g., PBX) in use today employ physical telephone units (referred to herein as “desksets”) that are wired into a switching device. The switching device, in conjunction with various processing components, provides a wide range of facilities and features to the deskset user. Such facilities and features include voicemail, call transfer, and conferencing, among others. The deskset is a user interface device that is typically comprised of a microphone/speaker, standardized telephone keypad, feature keys, text display, and other visual displays (e.g., lamps or LEDs), and is used primarily to receive and place telephone calls. The deskset employs a fixed and proprietary protocol for communicating with the switching device. Such protocols are typically restricted by the characteristics of the wire (i.e., the transmission path) that connects the deskset to the switching device.
Because the cost to acquire and maintain the switching device can be significant, many organizations choose to install a central switching device in a primary office, and allow users resident in remote offices to access the central switching device via extender links over the Public Switched Telephone Network (PSTN). This arrangement, however, can lead to unfortunate situations that consume unnecessary channel bandwidth in the extender link between the central and remote locations. For example, FIG. 1 shows a central office in city X with a PBX switch 10, and a remote office in city Y. The remote office in city Y utilizes the PBX 10 at the central office in city X through an extender 12 that communicates with a gateway 14 at the central office via an extender link 16 that exists, at least partially, within the PSTN. Suppose an outside phone 18 calls the direct inward dialing (DID) number associated with a user phone 20 in the remote office. The extender 12 will detect the incoming call and route the call to the PBX 10 via the gateway 14 and the extender link 16. The PBX 10 detects the incoming call and determines that it is for the user phone 20 at the remote office. The PBX 10 routes the call to the user phone 20 via the gateway 14, the extender link 16 and the extender 12. Note that channel bandwidth needed to be reserved on the extender link twice; once when the extender 12 routes the call to the PBX 10, and once when the PBX 10 routes the call back to the user phone 20. The bandwidth reserved on the extender link 16 is necessary only because the PBX 10 is located in a city different from the source and destination of the call.
The same path, only in reverse, occurs when the user 20 phone calls the outside phone 18. Further, since a call (in either direction) must traverse so many paths from city to city, the likelihood that at least one of the paths will be disrupted, thus disrupting the call) is greater than if the call remained completely in city Y.